Easy synthesis of new 2-oxo-2,3-dihydro-1H-pyrrolo[1,2-b]pyrazole systems

1,2-Diaza-1,3-butadienes react with dialkyl 1,3-acetonedicarboxylate in the presence of potassium carbonate to give 2-hydroxy-2,3-dihydro-1H-1-aminopy rroles that in turn produce 1-aminopyrroles by dehydration in the presence of copper(II) trifluoromethansulfonate. The treatment of these compounds wi th sodium hydride leads to NH-substituted 2-oxo-2,3-dihydro-1H-pyrrolo[1,2- b]pyrazole. Under the same reaction conditions, NH-BOC protected 1-aminopyr roles, after acidic cleavage of the BOC protecting group, afford NH-unsubst ituted 2-oxo-2,3-dihydro-1H-pyrrolo[1,2-b]pyrazole.